1. Field of the Invention
This invention relates to a frequency processing method for a radiation image for viewing, particularly for diagnostic purposes, and an apparatus for carrying out the method. This invention particularly relates to a method of reducing noise in a frequency processing for improving the image quality, particularly diagnostic efficiency and accuracy, of a radiation image, and an apparatus for carrying out the method.
By the term "frequency processing" as used herein is meant a processing for enhancement of frequency response, for example, an unsharp mask processing as disclosed in U.S. Pat. No. 4,315,318 and Japanese Unexamined Patent Publication No. 55(1980)-87953.
2. Description of the Prior Art
The frequency processing as described above is conducted for improving the image quality, particularly diagnostic efficiency and accuracy, of a radiation image. However, in the frequency processing, a problem arises as described below. That is, in radiation image information obtained by exposure to a radiation of low dose, radiation quantum noise becomes perceptible. When the radiation image information is directly subjected to the processing for enhancement of frequency response, a rough image wherein noise is enhanced is obtained and the image quality, particularly diagnostic efficiency and accuracy, is adversely affected by noise.
The degree of enhancement in the frequency processing is adjusted by an external input, for example manually, in accordance with the image recording portion of an object, the image recording method (contrasted image recording, tomography, etc.) or the like. In this case, it is impossible to cope with the effect of noise changing with the level of radiation exposure dose.